You may want to talk to John Polstra <jdp@FreeBSD.org> about PAM vs. BSD
Auth since he looked at both before deciding on PAM for FreeBSD (and the
client that paid him to do the work).  IIRC his major gripe with the BSD/OS
stuff is that the user interface for retrieving authentication information
is hard coded into the authentication provider.  This complicates things
like having an X application and a text based application use the same
auth module.

Just a data-point...

--
Justin